The present invention broadly concerns devices for use in spinal implant systems, particularly those using spinal rods contoured for connection at various locations along the length of the spinal column. More specifically, the invention concerns an apparatus for linking adjacent spinal rods in a top-loading and top-tightening fashion. This invention is particularly useful with methods and devices for posterior fixation of the spine.
Several techniques and systems have been developed for use in correcting and stabilizing spinal curvatures, and for facilitating spinal fusion in the case of spinal disorders or degenerative conditions. Typically, a pair of bendable rods are longitudinally disposed adjacent the vertebral column and are fixed to various vertebrae along the length of the spine by way of a number of fixation elements, such as hooks and screws.
Numerous spinal rod systems have been developed which provide transverse connectors for linking the adjacent spinal rods across the spinal midline to provide a rigid and stable construct. Most of these systems present one or more difficulties for spinal surgeons. Many of the devices are high profile which increases soft tissue trauma and surgical complications. Furthermore, in many of these prior systems the attachment mechanisms must be preloaded on the spinal rods which can require significant pre-operative planning and which virtually eliminates the opportunity to add connectors in situ.
One transverse connector system is the TSRH(copyright) CROSSLINK(copyright) of Danek Medical, Inc. The TSRH(copyright) CROSSLINK(copyright) utilizes a three point shear clamp mechanism which restricts motion between the rods in all directions, and particularly resists axial forces between rods and torsional moments about the axis of the rods. A quadrilateral construct is formed by laterally connecting the rods across the sagittal plane with rigid plates. The lateral connection reduces the loss of correction that can occur over time.
Rigid transverse connections between spinal rods are beneficial because they restrict rod migration and increase construct stiffness. In many cases involving multi-level fusion of the spine, these features are essential while solid bone fusion is accomplished. In the post-operative period before fusion occurs, a significant amount of motion can occur between the rods, wires and hooks, which can, for example, allow a scoliotic correction to decrease or the pelvis to de-rotate toward its previous, deformed position. By providing a rigid transverse connection between two spinal rods, the loss of correction can be reduced and a stiffer construct can be created which may enhance the promotion of a solid fusion. While the TSRH(copyright) CROSSLINK(copyright) provides an excellent construct, a need has remained for low profile devices which link adjacent spinal rods in a top-loading and top-tightening fashion with a minimum of components and steps.
In accordance with one aspect of the invention, a connector is provided for linking adjacent longitudinal members, such as spinal rods, engaged to a spine. The apparatus includes a bridge member sized to span at least a portion of the distance between the spinal rods. A pair of engaging members are connected to the bridge member, each including a receptacle configured to receive a longitudinal member- when the connector is disposed over the adjacent rods. The engaging members also include the fixation surface adjacent to the receptacle and configured for engaging a longitudinal member, and a thru-hole defined in the engaging member adjacent to the receptacle for receiving a wedge member. The thru-hole intersects the receptacle and is aligned at an angle such that as the wedge member is advanced through the thru-hole, the wedge member will bear against a rod initially disposed in the receptacle and push the rod against the fixation surface to engage the connector to the rod.
In one specific embodiment of the invention, the engaging members include elongated connecting portion which are received by a bore in the bridge member. The bridge member also includes a pair of engaging surfaces adjacent to and contiguous with a respective one of the bores for engaging a connecting portion. A second thru-hole defined in the bridge member intersects each one of the bores and is aligned at an angle such that as a wedge member is advanced through the second thru-hole, the wedge member will bear against the connecting portions and push each one against a corresponding one of the engaging surfaces.
In another specific embodiment, the bridge member defines a slot for receiving one of the connecting portions and a first fastener bore which intersects the slot. The connecting portion also defines a second fastener bore which is alignable with the first fastener bore of the bridge member when the connecting portion is inserted into the slot.
In some embodiments of this invention, the fixation surface includes a circular concavity which has a smaller radius than the radius of the longitudinal member. This provides three points of contact on each of the longitudinal members which restricts motion between the rods in all directions.
One object of the invention is to provide an apparatus for use in laterally connecting longitudinal members implanted adjacent a patient""s vertebral column. Another object of this invention is to provide an apparatus which restricts rod migration and increases overall construct rigidity.
One advantage of this invention is that it provides fixation assemblies that can be top loaded, or implanted over spinal rods after the spinal rods have been engaged to the spinal column. A further benefit is achieved by top-tightening aspects of the invention.
Another benefit of this invention is that it provides three points of contact on the spinal rod which restricts rod migration and increases overall construct rigidity.
Other objects and further benefits of the present invention will become apparent to persons of ordinary skill in the art from the following written description and accompanying figures.